1. Field of the Invention
This invention relates to thermoplastic poly(amide-urethane) block copolymers which are characterized by excellent flexibility at low temperatures and by good adhesion to a wide variety of surfaces.
2. Description of Related Art
Thermoplastic polymers have been successfully used in the production of hotmelt adhesives and are widely used in industry for bonding a variety of materials and surfaces. Copolymers based on ethylene and vinyl acetate, copolyamides based on caprolactam, copolyesters based on terephthalic acid and other polybasic carboxylic acids and various glycols, polyurethanes and polyester urethanes, and polyamides based on dimer acids have all been successfully used in this field. However, the requirements which these materials must satisfy are becoming increasingly more stringent so that modifications are frequently necessary. For example, it is frequently necessary to improve the properties of the starting materials by the addition of other polymers to a thermoplast base or by the incorporation of resins, plasticizers or other auxiliaries. In these modifications, particularly the modification of polyamides based on dimerized fatty acids, and optionally with the addition of sebacic acid and various amines, the thermoplast bases become incompatible, at certain desired temperature ranges, with other starting materials used for producing hotmelts.
U.S. Pat. No. 4,018,733 discloses a typical prior art hot melt adhesive composition comprising an acidic ethylene polymer, a polyamide, and a tackifier.
In order to obtain optimal properties, especially at low temperatures, and more particularly optimal properties for use in the adhesive field, the present invention seeks to solve the problem of reproducibly providing, by chemical modification, polyamides based on dimer acids and amines which do not have any of the above-mentioned disadvantages. More particularly, the invention seeks to provide block copolymers which are characterized by excellent adhesion to a wide variety of surfaces and which, in addition, have excellent flexibility at low temperatures. Finally, the invention seeks to provide block copolymers having excellent adhesion and cohesion properties and which afford corrosion protection to metals and wood.